Best Open Source SIEM

Open-source SIEM is a good fit if: you have engineering resources to deploy, configure, and maintain the platform; you have budget constraints that prevent commercial SIEM licensing; you have specific technical requirements that demand full control over the deployment. Open-source SIEM is a poor fit if: you lack dedicated security engineering resources; you want time-to-value under 30 days; or you need AI-assisted triage and investigation.

Open-source SIEM has zero licensing cost but significant engineering TCO: infrastructure costs (servers, storage, network), staff time to deploy and maintain (typically 20–40 hours initial setup plus 5–10 hours per week ongoing), detection engineering to build and tune detection rules, and operational overhead for upgrades and scaling. For small teams, the engineering cost often exceeds commercial SIEM licensing cost.

Wazuh is the most complete open-source SIEM option with active development, a broad detection rule library, and a good community. It provides host-based detection via its agent, compliance checking, and basic SIEM correlation. Compared to commercial SIEMs: Wazuh lacks ML-based UEBA, AI investigation, managed threat intelligence, and enterprise support SLAs. It is a viable choice for budget-constrained teams with engineering resources.

Yes. Sigma is a vendor-neutral detection rule format with compilers that output Wazuh rules, Elastic EQL, OpenSearch queries, Splunk SPL, and others. Using Sigma as your primary rule format means your detection content is portable across open-source and commercial platforms. Wazuh and Elastic Security both have community Sigma rule libraries.

Wazuh is a purpose-built SIEM that uses Elasticsearch for storage but adds SIEM-specific features: host-based agents, compliance checking, file integrity monitoring, and active response. The ELK Stack is a general-purpose log management platform that can be configured for security use cases with additional setup. Wazuh is easier to get to a working SIEM state out of the box; pure ELK requires more customisation.

A basic Wazuh deployment with agents on a handful of systems: 4–8 hours. A production-grade deployment with log pipelines, tuned detection rules, and dashboards: 2–4 weeks for an experienced engineer. Building the equivalent of an enterprise SIEM capability with open-source tools: 3–6 months of engineering time. Compare to commercial platforms that target 1–2 weeks to initial value.

The Sigma community provides thousands of detection rules for common attack techniques, compilable to Wazuh and Elastic formats. Wazuh has its own built-in rule library covering common attack patterns. Elastic Security includes a pre-built detection rule library. The quality and coverage of community rules varies — expect to tune extensively and add environment-specific rules over time.

Yes, but it requires significant infrastructure engineering. Elastic and OpenSearch both scale horizontally. Wazuh has Wazuh Indexer (Elasticsearch-based) for scale. The engineering effort to scale, tune, and operate a distributed open-source SIEM cluster at enterprise log volumes (100GB+/day) is substantial. At that scale, the infrastructure cost and engineering overhead often approaches or exceeds commercial SaaS SIEM costs.

Open-source SIEMs can satisfy compliance requirements for log collection, retention, and monitoring — if properly configured. Wazuh includes compliance packs for PCI DSS, HIPAA, GDPR, and CIS benchmarks. You will need to document your deployment, demonstrate active monitoring, and ensure log retention meets requirements. Third-party audit firms may require additional evidence compared to commercial platforms with built-in compliance reporting.

Signs you've outgrown open-source SIEM: alert volume exceeds analyst capacity and you can't keep up; your team is spending more time maintaining the platform than using it; you need AI investigation or autonomous triage; scaling is hitting infrastructure limits. The migration path typically goes to commercial SaaS SIEM or AI SOC platform. Choose a platform that supports Sigma rule import to preserve your detection content investment.